Glasses-free 3D smartphones are about to invade the U.S., with Sprint launching sales of the HTC Evo 3D on Friday and AT&T confirming that sales of the LG Thrill 4G will begin sometime later this summer.

Sprint said on June 6 that its 3D entry will go on sale June 24 at a cost $199.99 with a two-year service contract.

AT&T on Wednesday said it will make the LG Thrill available this summer, but it didn't name a price or an availability date.

An AT&T spokeswoman said in an interview that the LG Thrill will arrive "later this summer" and will be competitively priced. One person familiar with the pricing said it will sell for less than the HTC rival from Sprint.

The two phones have similar 3D features, but they also have some important differences.

In addition to offering 3D viewing without a need for glasses, both run on the fastest available networks from their respective carriers: Sprint's WiMax and AT&T's HSPA+. Also, both have 4.3-in. touchscreens and dual rear-facing stereoscopic cameras to capture 3D video content.

Among their differences, the HTC Evo 3D will run the Android 2.3 operating system, which gives it an advantage over the LG Thrill, which will initially run Android 2.2 but will later be upgraded to Android 2.3.

The HTC Evo 3D has a 1.2GHz dual-core processor, while the LG Thrill comes with a 1GHz dual-core processor that features two channels to connect to the phone's dual memory to improve performance. (LG has created a video to explain the capability on the LG Optimus, which is the same device as the LG Thrill but has a different name. The Optimus went on sale in the U.K. this week. )

The LG Thrill 3D smartphone from AT&T.

Both 3D devices were shown in March at the CTIA wireless trade show. Analysts said at the time that questions remained over how much demand there would be for a 3D experience on small devices. Many reviewers have called 3D smartphones novelties or gimmicks, but early Android adopters are expected to be especially keen on the devices.

Gamers will be the prime audience. They will likely be eager to take advantage of the fast networks and complex games that sometimes take place in real-time among multiple players in different locations.

The LG Thrill 4G from AT&T will come preloaded with a 3D button on the home screen that allows access to 3D games, 3D movies and user-created 3D content. It will be preloaded with access to YouTube 3D for viewing and uploading 3D content.

Jeff Bradley, senior vice president of devices at AT&T, acknowledged that consumer demand for 3D is "relatively nascent," but he added that the LG Thrill 4G "does 3D right and is also a superlative smartphone." He noted the importance of having 3D cameras on smartphones, saying user-generated content "has the power to shape the evolution of 3D."